Polyester-based strapping is commonly used in the packaging industry to combine, hold, reinforce, or fasten items. Commercial strapping requires a combination of physical properties that can be difficult to incorporate into a single composition in a cost-effective manner. For example, the strapping must have sufficient tensile strength along its longitudinal axis without being susceptible to significant lengthwise splitting. The strapping should maintain an initial tension over a period of time and concede minimal stress relaxation. As used herein stress relaxation is the loss of initial tension. Critically, the strapping must also exhibit sufficient tension retention which keeps the strapping tight around the load, even if the load settles, shifts, or shrinks in size. After being wrapped around an object, the strapping ends are drawn tightly together and fused to form a seal. Typically, the fused seal represents the weakest point of the strapping and, thus, the point most susceptible to failure. Under heavy loads the seal is usually more apt to separate when the strapping is snapped across its width upon being released from the sealing equipment. Thus, great seal strength at the fused ends and a resistance to splitting or breaking after sealing are critical properties of commercial strapping.
Pure polyester strapping is strong and inexpensive, but fails to provide a full range of above-indicated properties. Relatively costly polyolefin co-polymer additives have been added to polyester-based strapping to improve some of these properties, such as resistance to splitting, but these additives may not sufficiently improve other properties such as seal strength and tension retention. Certain additives may also discolor the strapping, (e.g., strapping made from polyethylene terephthalate (PET)), such as by turning it opaque or milky, which can interfere with the operation of the strapping equipment (e.g., optical sensors), and can also be less visually appealing to customers. Consequently, there remains a significant need to identify polyolefin co-polymer additives and new polyester strapping compositions with sufficient seal strength, tension retention, resistance to splitting, and maintenance of PET's traditional color and translucence.